Process of acetylating a specific kind of regenerated cellulose and recovering ingredients from the used acetylating bath



United States Patent PROCESS OF ACETYLATING A SPECIFIC KIND OF REGENERATED CELLULOSE AND RECOVER- ING INGREDIENTS FROM THE USED ACET- YLATING BATH Jean Fraizy and Gerard Finiels, Lyon, France, assignors to Societe Rhodiaceta, Paris, France, a corporation of France No Drawing. Filed Sept. 26, 1960, Ser. No. 58,312

Claims priority, application France, Oct. 2, 1959, 806,620; June 10, 1960, 829,632 6 Claims. (Cl. 8121) This invention relates to certain new textile articles of cellulose acetate and to their production.

Articles made of acetylated cotton or acetylated regenerated cellulose have long been known. They are obtained by acetylating cotton or regenerated cellulose without passing through the solution stage by causing acetic anhydride to react on the cellulose fibres in the presence of a catalyst and of a diluent which is miscible in any proportion and at any temperature with the anhydride, especially benzene, toluene, xylene and amyl acetate. This method of acetylation is usually designated heterogeneous acetylation.

As is known, acetylated cottons have a reduced dyeing affinity, and the acetylated regenerated celluloses so far known do not have a fibrillar structure.

The present invention provides new textile articles of an acetylated regenerated cellulose having a fibrillar structure.

These new articles are characterised in that they conform simultaneously to the following four characteristics:

(a) Their proportion of combined acetic acid is between 45 and 62.5% reckoned as acetic acid,

(b) They are insoluble in acetone,

(c) The form of their transverse section is that of filaments and fibres of regenerated cellulose,

((1) Their microstructure is an oriented fibrillar structure.

The fibrillar microstructure of the new cellulose acetate fibres can be shown by proceeding as follows:

A single strand previously swelled with a 50% by volume water-acetone mixture at C., which strand has been slightly crushed while resting on the cover glass, is examined under a microscope. A fibrillar structure is then observed.

The cellulose acetate fibres having all these characteristics can be obtained, by processes which are also novel and which are hereinafter described, especially but by no means exclusively from regenerated cellulose fibres known as Polynosic fibres characterized by an oriented fibrillated microstructure, a minimum wet strength in the order of 2.2 grams per denier and a wet elongation of less than 3.5% at a stress of 0.5 gram per denier. Ac cording to Tachikawa, the degree of polymerization of these fibers ranges from about 350 to upwards of 750. These fibers are described in the journals: Rayon Ze1lwolle September 1959, page 567, and Fachorgan fur Textilveredlung 14, 1959, No. 8, page 498, as well as Tachikawa U.S. Patent 2,732,279 and Kenyon et al. US. Patent 3,124,860. They form new articles of great techni cal interest, in that they are highly resistant to wear, their total strength is as good as before acetylation, and the elongation at break is even improved, which is quite unexpected. They are easily dyed in a very homogeneous manner throughout the thickness of the strands.

In one method of making the new fibres one part of regenerated cellulose is acetylated in at least parts of a bath containing 50100% of acetic anhydride and 50- 0% of an inert organic liquid diluent, using as catalyst an acetate of an alkali metal in a quantity such that when 3,215,490 Patented Nov. 2, 1965 the acetylation is completed the bath does not contain more than 2% by weight of free acetic acid.

As acetylation catalyst, sodium acetate, potassium acetate or lithium acetate is preferably used. It has been found that by carefully regulating firstly the quantity of acetylation bath in relation to the regenerated cellulose and-secondly the quantity of catalyst, it is possible to keep to a very small percentage the quantity of free acetic acid in the acetylation bath, this making it possible to preserve particularly the strength and the structure of the original cellulose.

If the quantity of catalyst is sufficiently high, it is even possible to fix practically all the acetic acid which is formed as the acetylation prorgesses.

The catalyst can be added directly to the acetylation bath or can be incorporated into the regenerated cellulose prior to the acetylation.

As the inert diluent there may be used for example benzene, toluene, xylene, carbon tetrachloride, tetrachlorethylene, perchlorethylene or amyl acetate. The quantity of diluent can be considerably below 50% of the bath and it can even be omitted entirely.

In another method of making the new fibres the acetylation bath is a mixture of acetic anhydride with a diluent which is immiscible with it at ambient temperature but becomes miscible at higher temperatures, and the acetylation is effected at a temperature at which the anhydride and the diluent are miscible. For the sake of simplicity, such diluents will hereinafter be referred to as diluents with potential miscibility.

It is to be noted that until the present invention was made, heterogeneous acetylation had only been achieved by causing acetic anhydride to react on the cellulose in the presence of a catalyst and a diluent miscible in all proportions and at ambient temperature with this anhydride, such as benzene, toluene, xylene, amyl acetate, carbon tetrachloride, trichlorethylene and perchlorethylene.

As in the first method described, an alkali metal acetate, especially the acetate of sodium, potassium or lithium can be used as catalyst as already known. The catalyst is preferably incorporated into the cellulose prior to the acetylation.

As diluents with potential miscibility with acetic anhydride, there are preferably employed organic liquids which become miscible with the anhydride at a temperature higher than 50 C. Particularly useful diluents include decahydronaphthalene, whose miscibility point is in the region of C., and white spirit, whose miscibility point is in the region of 70 C. Carbon disulphide and cyclohexane can also be used.

In order to obtain good results, it is preferred that the ratio:

weight of acetylation bath weight of cellulose be at least 10: 1; the ratio:

weight of diluent weight of anhydride can advantageously be between 3:7 and 8:2, the most advantageous ratios being between 2:3 and 3:2.

A judicious choice of this ratio permits of an improvement being obtained in the appearance of the resulting articles.

Cooling of the bath to below the miscibility point of the diluent after completing the acetylation causes a separation into two layers, one of which contains practically all the diluent and the other practically all the anhydride which has not reacted and the acetic acid which has formed during the reaction. This possibility of separating the constituents of the acetylation bath greatly facilitates subsequent operations. The recovery and the separation of the excess anhydride and the acetic acid produced in the reaction can be carried out much more easily than in the conventional processes, which require a complete rectification of a homogeneous mixture. This recovery is made easier by the fact that the distillation temperatures of the diluents referred to above are widely spaced from the boiling points of the acetic acid and anhydride. It is known that the distillation temperature of decahydronaphthalene is in the region of 193 C. and that of white spirit is between 150 and 210 C. (Chemical Dictionary of Clement Duval, Paris, 1959), as compared with 118 C. for acetic acid and 140 C. for acetic anhydride.

When the acetylation is carried out in the presence of decahydronaphthalene or white spirit as diluent there is very little swelling of the fibre during the acetylation, and this makes it possible for acetylation to be carried out for a longer time or at a higher temperature when it is desired to obtain a high degree of acetylation, while preserving the good mechanical and textile properties of the cellulose fibres.

The heterogeneous acetylation can be effected at any desired stage, continuously or discontinuously, either on threads with continuous filaments, or on fibres in the form of tows, slivers, rovings or the like, or on spun yarns, or on woven or knitted fabrics or made-up articles.

The acetylation can also be carried out on articles containing a certain percentage of another fibre, which is capable of resisting the acetylation treatment.

Cloths and fabrics prepared from the acetylated threads or fibres of the invention are very resistant to creasing. They can be very easily washed and their afiinity for dyeing with plasto-soluble dyes is excellent.

The form of the transverse section of the acetylated fibres is similar to that of the fibres before acetylation.

The following examples illustrate the invention without of course limiting it in any way.

Example I 100 parts of continuous Polynosic regenerated cellulose threads were acetylated for 2% hours at 50 C. in a bath consisting of Parts Acetic anhydride 2000 Perchlorethylene 1000 Sodium acetate 150 After the acetylation, the content of free acetic acid in the bath was 0.1%.

The combined acetic acid content of the acetylated threads was 50% and their transverse section was circular. The threads had a fibrillar microstructure and excellent resistance to wear, and were dyed with plasto-soluble dyes throughout their thickness.

Example 11 180 parts of Polynosic regenerated cellulose staple fibre impregnated with 80 parts of potassium acetate were acetylated for 2 hours at 98 in the following mixture:

Parts Acetic anhydride 2000 Perchlorethylene 1500 100 parts of a 3000 denier tow of continuous Polynosic regenerated cellulose filaments having a degree of polymerisation of 520 were treated for 1 hour in an aqueous solution of potassium acetate of 500 g./l. After being centrifuged and dried, the filaments contained 78% of potassium acetate.

The filaments were acetylated in 2500 parts of acetic anhydride at C. without any other addition. At the end of the acetylation, the bath contained only 1.2% of free acetic acid.

Products having the following characteristics were obtained:

Acetylation time Nonacetylated comparison 2 hours 5 hours material Denier (total count) 4, 300 4, 550 3, 000 Total dry strength in g 10, 700 11, 000 10, 700 Elongation, percent 10. 6 13.6 7. 4 Content of combined acetic a cent 50 51 0 The filaments obtained had an excellent resistance to wear and a fibrillar structure, and their transverse section was circular. Furthermore, as shown in the table, their total strength was maintained and their elongation at break was greater than that of the un-acetylated filaments.

Example IV 100 parts of continuous Polynosic regenerated cellulose filaments were treated for 1 hour at 30 C. in an aqueous solution containing 550 g. of potassium acetate per litre. After centrifuging and drying at 60 C., the filaments contained of potassium acetate. They were then acetylated for 2 hours at C. in a mixture of 1500 parts of acetic anhydride and 1500 parts of toluene. After the acetylation, the bath contained only 0.9% of free acetic acid.

The acetylated filaments had the following characteristics as compared with un-acetylated filaments:

After Before acetylation acetylation Denier (total count) 620 400 Content of combined acetic acid percent 54 0 Total dry strength in g 1,984 2,000 Dry elongation, percent 0 7.8

The filaments were completely insoluble in acetone. Their resistance to flexion was 10 times better than that of ordinary cellulose acetate filaments and they had a marked fibrillar structure.

Example V 220 parts of discontinuous Polynosic regenerated cellulose fibres containing parts of potassium acetate were acetylated for 2 hours at 100 C. in a mixture of 3000 parts of acetic anhydride and 1000 parts of xylene. After the acetylation the bath contained only 0.3% of free acetic acid.

The resulting acetylated fibres had a fibrillar structure and a combined acetic acid content of 53%; their resistance to wear was excellent.

Example VI The bath remaining after the acetylation was cooled to 50 C., whereupon it separated clearly into two layers having respectively the following compositions:

Upper layer: Percent Decahydronaphthalene 95 Acetic anhydride 2 Acetic acid 3 Lower layer:

Decahydronaphthalene 0.8 Acetic anhydride 70 Acetic acid 29.2

After skimming 01f (topping) only 2% and fortifying with acetic anhydride, the upper layer could be used again directly. For this fortification the lower layer B was used, after rendering it substantially free from acetic acid by distilling 011 30% of its weight.

Example VII A flock or wad of Polynosic regenerated cellulose fibre containing 65% of potassium acetate was acetylatedfor 2% hours at 95 C. in a bath composed of 45% of acetic anhydride and 55% of white spirit.

After the acetylation, the bath was filtered and cooled to 20 C., and the acetic anhydride on the one hand and the white spirit on the other hand were recovered after topping and elimination of the acetic acid formed during the reaction, as described in Example VI.

The acetylated flock was thoroughly washed and dried. Its content of combined acetic acid was 57.4%. The mean breaking load of the treated fibres was substantially equal to that of the initial fibres.

Example VIII 100 parts of continuous filaments of regenerated cellulose of the ordinary viscose type were treated for 1 hour in a solution containing 500 g. of potassium acetate per litre. After centrifuging and drying, the filaments, which now contained 60% of this salt, were acetylated for 1% hours at 100 C. in the following mixture:

Parts Acetic anhydride 2000 Toluene 2000 After the acetylation, the bath contained only 0.95% of free acetic acid.

The resulting filaments had a combined acetic acid content of 54%, and their transverse section was serrated; they had a total strength of 300 g., as compared with 306 g. before acetylation, and a dry elongation of 24%.

Their mechanical qualities were very satisfactory.

Example IX 100 parts of cellulose fibres of the same type were acetylated for 2 hours at 95 C. in a bath formed of:

Parts Acetic anhydride 1500 Toluene 1500 Lithium acetate 100 After the acetylation, the content of free acetic acid in the bath was 0.6%.

The combined acetic acid content of the acetylated fibres was 45 and their transverse section was serrated. They dyed very satisfactorily with plasto-soluble dyes.

Example X One part of spun staple fibre regenerated cellulose yarn of normal structure and containing 70% of potassium acetate was acetylated in parts of a mixture consisting of 50% of acetic anhydride and 50% of decahydronaphthalene. The acetylation was carried out at 80 C. for

2 hours. After the acetylation, separation of the acetylation mixture, and washing and drying of the spun yarn, the latter had a combined acetic acid content of 50.4%. The acetylation mixture was cooled to 20 C., this causing its separation into two distinct layers in less than 10 minutes.

The elimination of the acetic acid formed during the reaction could be carried out just as easily as in Example VI.

We claim:

1. Process for the production of textile articles which comprises acetylating an article comprising fibres of regenerated cellulose having an oriented fibrillar microstructure, a minimum wet strength in the order of 2.2 grams per denier and a wet elongation of less than 3.5% at a stress of 0.5 gram per denier in an acetylating bath containing acetic anhydride and an inert liquid organic diluent which is a non-solvent for cellulose acetate of the combined acetic acid content being produced and which is completely miscible with acetic anhydride to form a homogeneous mixture only at temperatures above 50 C., the acetylation being effected at a temperature above 5 0 C. at which the anhydride and diluent are so miscible, and until the combined acetic acid content of the product is 4562.5% reckoned as acetic acid to give an acetoneinsoluble product, using as catalyst an alkali metal acetate in amount such that at the end of the acetylation the bath contains at most 2% of free acetic acid, separating the acetylated textile article from the bath, cooling the bath to a temperature at which the anhydride and diluent are immiscible so as to cause it to separate into a layer consisting mainly of diluent and a layer consisting mainly of acetic anhydride and acetic acid, and recovering the diluent by simple decantation.

2. Process according to claim 1, which includes also the step of employing the separated diluent in the acetylation of further textile material after fortifying it with acetic anhydride.

3. Process according to claim 2, wherein potassium acetate is used as acetylation catalyst.

4. Process according to claim 1, wherein the weight ratio acetylation bathzregenerated cellulose is at least 10:1, and the weight ratio diluentzacetie anhydride is between 2:3 and 3:2.

5. Process according to claim 1 wherein the diluent is decahydronaphthalene.

6. Process according to claim 1 wherein the diluent is white spirit.

References Cited by the Examiner UNITED STATES PATENTS NORMAN G. TORCHIN, Primary Examiner.

MORRIS O. WOLK, ABRAHAM H. WINKELSTEIN,

Examiners. 

1. PROCESS FOR THE PRODUCTION OF TEXTILE ARTICLES WHICH COMPRISES ACETYLATING AN ARTICLE COMPRISING FIBRES OF REGENERATED CELLULOSE HAVING AN ORIENTED FIBRILLAR MICROSTRUCTURE, A MINIMUM WET STRENGTH IN THE ORDER OF 2.2 GRAMS PER DENIER AND A WET ELONGATION OF LESS THAN 3.5% AT A STRESS OF 0.5 GRAM PER DENIER IN AN ACETYLATING BATH CONTAINING ACETIC ANHYDRIDE AND AN INERT LLIQUID ORGANIC DILUENT WHICH IS A NON-SOLVENT FOR CELLULOSE ACETATE OF THE COMBINED ACETIC ACID CONTENT BEING PRODUCED AND WHICH IS COMPLETELY MISCIBLE WITH ACETIC ANHYDRIDE TO FORM A HOMOGENEOUS MIXTURE ONLY AT TEMPERATURES ABOVE 50*C., THE ACETYLATION BEING EFFECTED AT A TEMPERATURE ABOVE 50*C. AT WHICH THE ANHYDRIDE AND DILUENT ARE SO MISCIBLE, AND UNTIL THE COMBINED ACETIC ACID CONTENT OF THE PRODUCT IS 45-62.5% RECKONED AS ACETIC ACID TO GIVE AN ACETONEINSOLUBLE PROCUT, USING AS CATALYST AN ALKALI MEAL ACETATE IN AMOUNT SUCH THAT AT THE END OF THE ACETYLATION THE BATH CONTAINS AT MOST 2% OF FREE ACETIC ACID, SEPARATING THE ACETYLATED TEXTILE ARTICLE FROM THE BATH, COOLING THE BATH TO A TEMPERATURE AT WHICH THE ANHYDRIDE AND DILUENT ARE IMMISCIBLE SO AS TO CAUSE IT TO SEPARATE INTO A LAYER CONSISTING MAINLY OF DILUENT AND A LAYER OF CONSISTING MAINLY ACETIC ANHYDRIDE AND ACETIC ACID, AND RECOVERING THE DILUENT BY SIMPLE DECANTATION. 